Quotes from Erin and Sara Foster About Their Stepmom Katharine McPhee

Katharine McPhee might be younger than her stepdaughters Erin Foster and Sara Foster, yet they share a strong connection.

The American Idol alum began her relationship with David Foster in 2017, and they got engaged a year later. In June 2019, the couple said “I do” in London. In October 2020, it was announced that McPhee was expecting, and their son Rennie was born in February 2021.

Despite facing criticism for their 35-year age difference, David and McPhee’s relationship is supported by his children.

“Everyone has an opinion about something,” Sara remarked during a June 2026 appearance on Kristin Cavallari’s “Let’s Be Honest” podcast. “They’re 12 years in, and they are happy. … She’s a fully consenting woman; she is not some child bride. She is in her 40s.”

David is a father to six children, including Rennie. His eldest daughter, Allison, was adopted after birth but reconnected with him in adulthood. He shares daughter Amy with ex-wife B.J. Cook and three children—Sara, Erin, and Jordan—with ex-wife Rebecca Dyer.

Scroll down to see what Erin and Sara have to say about McPhee:

July 2018

After her father’s proposal, Sara affectionately referred to McPhee as “Mommmyyy” on Instagram.

September 2018

The siblings humorously shared with Us that they “hope[d]” to receive wedding invites from their dad.

Sara told Us that David “never looked better” while with McPhee, adding, “He’s so happy. He doesn’t age. I asked him the other day, ‘Are you on HGH? What’s going on?’ He looks incredibly youthful.” Erin jokingly suggested that David’s “young fiancée” should take all the credit.

February 2019

Sara described her future stepmom as “really funny” in an exclusive statement to Us. “Katharine really holds her tongue. If I were her, I’d be combating trolls all day. I wouldn’t even have time for Broadway.”

While rumors swirled about McPhee and David’s extravagant wedding expenses, Erin quipped on Instagram, “There goes my inheritance.”

May 2019

“We love our future stepmom,” Sara told Us, expressing excitement for her dad’s happiness.

August 2019

The sisters mentioned at an event that they “fully expect [McPhee] to have a child and completely support it.” (McPhee later welcomed son Rennie with David in February 2021.)

September 2019

“Honestly, we truly love Katharine,” Erin shared exclusively with Us. “It takes a strong and graceful person to step into a family as the fifth wife, especially when her adult daughters are older than her. She makes it easy for us to connect as a family, and we’re grateful for her.”

October 2019

Sara clarified to Us that McPhee wasn’t pregnant yet, although she believed “of course she wants a baby. I’m sure they’ll have one.”

November 2019

At an event, she called her dad and McPhee the “perfect couple,” stating exclusively to Us Weekly, “I don’t think they’ve ever fought. It’s beautiful to watch.”

April 2021

“Ever done side planks with your 37-year-old stepmom?” Erin posted on her Instagram Story. “I have.”

May 2021

“Happy first mama’s day to Rennie’s mom,” Sara wrote on an Instagram Story post.

July 2021

Erin likened her and Katharine’s July 2021 workout with Amanda Kloots to “death.”

December 2021

“If I can accept my stepmom looking like this, everyone else should too,” Erin commented on an Instagram post featuring McPhee’s post-baby bikini body. “The photo [my dad posted] was neither altered nor filtered, and she hasn’t had surgery. You can’t shame someone for feeling good after having a baby.”

July 2022

Erin playfully teased her stepmom on Instagram after she shared a steamy post with David: “Poor guy … too bad he doesn’t get much attention,” McPhee captioned her pictures, to which Erin replied, “Reporting this.”

December 2022

Erin supported the “My Grown-Up Christmas List” singer and praised her bold style after noticing McPhee’s stunning green gown from Vegas. “Okkkkkkkk 🔥,” commented the TV writer on Instagram.

February 2023

After McPhee shared a set of throwback photos from her life with David, Erin responded quickly with a heartwarming message. “It was always you. Happy 💕 day,” the Smash alum wrote, to which Erin commented, “😭😭❤️❤️.”

June 2026

Sara defended David and McPhee’s relationship in the face of critics regarding their age difference, praising her “amazing” stepmom.

“Being a stepparent is challenging. You aim to get along with your partner’s children while also respecting the biological mother,” Sara said. “But she navigates this beautifully.”

She added, “I think it’s a delicate balance, and she handles it very well.”

July 2026

Sara lauded McPhee as “fantastic” on “The Morgan Stewart Show” podcast.

“She’s so gorgeous, and I absolutely adore her,” Sara proclaimed. “She even taught my 10-year-old how to ride a bike.”